Hi,
Doing a song that a student likes is always great. Being a teacher, you can't always do that, because part of piano lessons is learning that sometimes you have to learn a song that you just don't feel like learning. That's why the great pianists are so disciplined. I find that throwing in a fun song on a regular basis keeps them interested. When they start, I ask them what a few of their favorite songs are. That gives me an idea of what genre to look for, such as popular, classical, jazz, rock.... I like to take a short break from the method lesson book when it seems they are falling off pace or after they've completed a lesson book. The summer is a good time to do this too. I use the Faber and Faber series and they make it so easy to do this because they have a whole set of books that are just for this purpose and for every level! They have popular, classical, jazz, rock and roll, children's song, hymns. Have them pick the book they like. They don't even have to do all the songs. Just spend a month or so on it and then get back into learning new things. You could even have all your students take their "break" at the same time and then have them each pick their favorite song from their book and have a mini-recital with everyone. Every student is different, you just have to ask the questions and they will answer. "Did you like that song?" They will be honest with you. I had a student walk in and the first thing out of her mouth was, "You know that song you gave me? I hate it!" She's never like that, so I took a long look at the song and decided it wasn't worth it and skipped it. Show them that you enjoying playing and want them to enjoy playing. They will see it, understand it and respond.
Always have fun!
Denise <><